The present invention relates to a power window driving apparatus adapted to stop or reverse quickly the driving of a power window equipped on a vehicle in the event that the a jamming of an obstacle by the power window occurs while the power window is being driven, and more particularly to a technique for ensuring the protection of a circuit even in the event that positive and negative terminals of a battery are connected inversely.
In power windows equipped on a vehicle, window glasses are raised or lowered by applying a battery voltage to driving motors reversibly so as to switch the rotation of the driving motors between normal and reverse directions.
In addition, during the operation of the power window, there may occur a case where an obstacle is seized by the window glass, resulting in a trouble where, in case the obstacle is part of the occupant, the occupant gets injured unexpectedly or in case the obstacle is an implement, the implement gets damaged.
In order to solve the problem like this, as described in, for example, JP-A-2002-295129 (FIG. 3), there is proposed a technique for avoiding a trouble associated with the jamming of an obstacle by the window glass by stopping or reversing the window glass when detecting the jamming of an obstacle by the window glass in the event that the jamming of an obstacle by the window glass actually happens.
FIG. 3 is a circuit diagram showing the configuration of a power window driving apparatus described in the JP-A-2002-295129 As shown in the diagram, this driving apparatus includes a driving motor M101 for raising or lowering a window glass and a relay RY101 for enabling the application of a battery voltage VB to the driving motor M101 in such a manner that the polarity of the battery voltage VB can be switched so as to drive to rotate the driving motor reversibly. The relay RY101 includes FETs (T102), (T103) for normal rotating operation and reverse rotating operation, respectively.
Furthermore, the driving apparatus includes a shunt resistance R101 interposed between the power supply V1B and the driving motor M101 for detecting an excess current when the excess current is actually generated and an FET (T101) interposed between the driving motor M101 and a ground for stopping the supply of voltage to the driving motor M101 so as to stop raising or lowering a window glass when an excess current is actually generated.
In addition, the driving apparatus includes a current detection circuit which includes the shunt resistance R101 and a current limiting circuit which includes the FET (T101), and as shown in the diagram, the current detection circuit has comparators CMP11, CMP12, FETs (T121), (T122), resistances R120 to R125, R128, capacitors C11, C12 and a diode D121.
Additionally, the current limiting circuit includes a comparator CMP13, FETs (T131), (T132), resistances R131 to R137, a diode D131 and a NOR circuit NOR11.
Furthermore, the driving apparatus includes an OR circuit OR11, AND circuits AND1, AND2, a flip-flop circuit and a counter circuit.
Then, in the event that there occurs a jamming by the window glass while the driving motor M101 is being driven to rotate to thereby increase a current ID which flows to the driving motor M101, since a current Iref-f flowing to the FET (T122) is increased and a current Iref-s is slow to follow the increase in the current ID, an output signal of the comparator CMP12 becomes an L level, whereby an output signal of the NOR circuit NOR11 becomes an H level, and the FET (T131) is switched on, whereas the FET (T101) is switched off. As a result, the driving of the driving motor M101 is stopped.
Thereafter, the voltage of a positive side input terminal of the comparator CMP13 is increased by switching off the FET (T101), and an output signal of the comparator CMP13 changes to an H level, whereby an output signal of the NOR circuit NOR11 becomes an L level, and the FET (T131) is switched off, whereas the FET (T101) is switched on. Namely, the voltage supply to the driving motor M101 is started.
In the event that an excess current is generated in the current ID which still flows to the driving motor in this state, the above operation is repeated. Namely, the switching on and off of the FET (T101) is repeated. Then, the number of times of such repetition is counted by a counter, and in the event that the operation is repeated a predetermined number of times or more, it is determined that the jamming of an obstacle by the window glass is occurring, output signals to the AND circuits AND1, AND2 are stopped so as to stop the relay RY101, whereby the driving of the driving motor M101 is stopped.
According to the configuration, when the jamming of an obstacle by the window glass occurs to thereby increase a load current, the driving of the window glass can be stopped certainly.
In the technique described in JP-A-2002-295129, however, no countermeasures against an erroneous opposite connection to the battery to be taken. Namely, there may occur a case where the user or mechanic makes an erroneous opposite connection to the terminals (positive and negative) of the battery, and in order to deal with the case like this, a protection circuit needs to be equipped on electronic/measuring instruments and power equipment to protect them against damage even in the event that an erroneous opposite connection is made to the battery.
In the circuit shown in FIG. 3, a method is conceived in which a diode is provided between the FET (T131) and the ground (a position indicated by reference character B) or between the battery power supply terminal (positive) and the control circuit power supply (a position indicated by reference character A).
Here, in the event that a diode is placed at the position indicated by the reference character B, the drain voltage of the FET (T131) is increased by an extent to which the voltage is dropped by the diode (for example, 0.7 volt), causing a case where the FET (T101) cannot be switched off. In order to deal with this, while a method is conceived in which a diode is interposed between the FET (T101) and the ground, the placement of a diode for large current eventually calls for the enlargement in size of the apparatus and increase in costs and therefore it is not practical.
In addition, in the event that a diode is placed at the position indicated by the reference character A, a voltage coinciding with a voltage generated in the shunt resistance R101 cannot be generated in the resistance R120 due to a voltage drop by the diode so placed, causing a problem that a highly accurate control cannot be attained.